Atomic layer deposition methods and structures thereof

ABSTRACT

A method and structure for providing a pre-deposition treatment (e.g., of a work-function layer) to accomplish work function tuning. In various embodiments, a gate dielectric layer is formed over a substrate, and a work-function metal layer is deposited over the gate dielectric layer. The work-function metal layer has a first thickness. A pre-treatment process of the work-function metal layer may then performed, where the pre-treatment process removes an oxidized layer from a top surface of the work-function metal layer to form a treated work-function metal layer. The treated work-function metal layer has a second thickness less than the first thickness. In various embodiments, after performing the pre-treatment process, another metal layer is deposited over the treated work-function metal layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/244,103, filed Oct. 20, 2015, the entirety of which is hereby incorporated by reference.

BACKGROUND

The electronics industry has experienced an ever increasing demand for smaller and faster electronic devices which are simultaneously able to support a greater number of increasingly complex and sophisticated functions. Accordingly, there is a continuing trend in the semiconductor industry to manufacture low-cost, high-performance, and low-power integrated circuits (ICs). Thus far these goals have been achieved in large part by scaling down semiconductor IC dimensions (e.g., minimum feature size) and thereby improving production efficiency and lowering associated costs. However, such scaling has also introduced increased complexity to the semiconductor manufacturing process. Thus, the realization of continued advances in semiconductor ICs and devices calls for similar advances in semiconductor manufacturing processes and technology.

For example, as metal gate electrodes and high-K gate dielectrics have replaced traditional polysilicon gate electrodes and silicon dioxide dielectrics, one of the key challenges has been to find metal electrode layers having appropriate work function values. To that end, a variety of metal electrode layers, and combinations thereof, having a variety of work function values (e.g., near a conduction band-edge, near a valence band-edge, or near mid-gap) have been investigated for application in a variety of device types (e.g., 2D and/or 3D N-type/P-type FETs). Generally, much attention has been devoted to various work function tuning techniques. However, in at least some existing processes, the effective work function of a given metal layer is limited by lack of an adequate tuning knob. Some traditional work function tuning approaches merely adjust a thickness of the metal layer. For example, a thicker metal layer may be at times used in an effort to overcome work function metal loading effects. Additionally, in some existing processes, poor metal layer deposition may cause gaps or voids in the metal layer, detrimentally impacting device performance.

Thus, existing techniques have not proved entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A is a cross-sectional view of an MOS transistor according to some embodiments;

FIG. 1B is perspective view of an embodiment of a FinFET device according to one or more aspects of the present disclosure;

FIG. 2 is a flow chart of a method of performing a pre-deposition treatment of a work-function layer, in accordance with some embodiments;

FIG. 3 is a cross-sectional transmission electron microscope (TEM) image for a device processed without performing the pre-deposition treatment method of FIG. 2;

FIG. 4 is a cross-sectional TEM image for a device processed according to the pre-deposition treatment method of FIG. 2; and

FIG. 5 is a schematic top-view diagram of an exemplary multi-chamber processing system, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

It is also noted that the present disclosure presents embodiments in the form of methods of gate stack formation and related gate stack structures, which may be employed in any of a variety of device types. For example, embodiments of the present disclosure may be used to form gate stacks suitable for use in planar bulk metal-oxide-semiconductor field-effect transistors (MOSFETs), multi-gate transistors (planar or vertical) such as FinFET devices, gate-all-around (GAA) devices, Omega-gate (Ω-gate) devices, or Pi-gate (Π-gate) devices, as well as strained-semiconductor devices, silicon-on-insulator (SOI) devices, partially-depleted SOI devices, fully-depleted SOI devices, or other devices as known in the art. In addition, embodiments disclosed herein may be employed in the formation of P-type and/or N-type devices. One of ordinary skill may recognize other embodiments of semiconductor devices that may benefit from aspects of the present disclosure. For example, some embodiments as described herein may also be applied to the formation of contacts, vias, or interconnects.

With reference to the example of FIG. 1A, illustrated therein is an MOS transistor 100, providing an example of merely one device type which may include embodiments of the present disclosure. It is understood that the exemplary transistor 100 is not meant to be limiting in any way, and those of skill in the art will recognize that embodiments of the present disclosure may be equally applicable to any of a variety of other device types, such as those described above. The transistor 100 is fabricated on a substrate 102 and includes a gate stack 104. The substrate 102 may be a semiconductor substrate such as a silicon substrate. The substrate 102 may include various layers, including conductive or insulating layers formed on the substrate 102. The substrate 102 may include various doping configurations depending on design requirements as is known in the art. The substrate 102 may also include other semiconductors such as germanium, silicon carbide (SiC), silicon germanium (SiGe), or diamond. Alternatively, the substrate 102 may include a compound semiconductor and/or an alloy semiconductor. Further, in some embodiments, the substrate 102 may include an epitaxial layer (epi-layer), the substrate 102 may be strained for performance enhancement, the substrate 102 may include a silicon-on-insulator (SOI) structure, and/or the substrate 102 may have other suitable enhancement features.

The gate stack 104 includes a gate dielectric 106 and a gate electrode 108 disposed on the gate dielectric 130. In some embodiments, the gate dielectric 106 may include an interfacial layer such as silicon oxide layer (SiO₂) or silicon oxynitride (SiON), where such interfacial layer may be formed by chemical oxidation, thermal oxidation, atomic layer deposition (ALD), chemical vapor deposition (CVD), and/or other suitable method. In some examples, the gate dielectric 106 includes a high-k dielectric layer such as hafnium oxide (HfO₂). Alternatively, the high-k dielectric layer may include other high-k dielectrics, such as TiO₂, HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂, LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON), combinations thereof, or other suitable material. High-K gate dielectrics, as used and described herein, include dielectric materials having a high dielectric constant, for example, greater than that of thermal silicon oxide (˜3.9). In still other embodiments, the gate dielectric 106 may include silicon dioxide or other suitable dielectric. The gate dielectric 106 may be formed by ALD, physical vapor deposition (PVD), oxidation, and/or other suitable methods. In some embodiments, the gate electrode 108 may be deposited as part of a gate first or gate last (e.g., replacement gate) process. In various embodiments, the gate electrode 108 includes a conductive layer such as W, TiN, TaN, WN, Re, Ir, Ru, Mo, Al, Cu, Co, Ni, combinations thereof, and/or other suitable compositions. In some examples, the gate electrode 108 may include a first metal material for an N-type transistor and a second metal material for a P-type transistor. Thus, the transistor 100 may include a dual work-function metal gate configuration. For example, the first metal material (e.g., for N-type devices) may include metals having a work function substantially aligned with a work function of the substrate conduction band, or at least substantially aligned with a work function of the conduction band of a channel region 114 of the transistor 100. Similarly, the second metal material (e.g., for P-type devices) may include metals having a work function substantially aligned with a work function of the substrate valence band, or at least substantially aligned with a work function of the valence band of the channel region 114 of the transistor 100. Thus, the gate electrode 104 may provide a gate electrode for the transistor 100, including both N-type and P-type devices. In some embodiments, the gate electrode 108 may alternately or additionally include a polysilicon layer. In various examples, the gate electrode 108 may be formed using PVD, CVD, electron beam (e-beam) evaporation, and/or other suitable process. In some embodiments, sidewall spacers are formed on sidewalls of the gate stack 104. Such sidewall spacers may include a dielectric material such as silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, or combinations thereof.

The transistor 100 further includes a source region 110 and a drain region 112 each formed within the semiconductor substrate 102, adjacent to and on either side of the gate stack 104. In some embodiments, the source and drain regions 110, 112 include diffused source/drain regions, ion implanted source/drain regions, epitaxially grown regions, or a combination thereof. The channel region 114 of the transistor 100 is defined as the region between the source and drain regions 110, 112 under the gate dielectric 106, and within the semiconductor substrate 102. The channel region 114 has an associated channel length “L” and an associated channel width “W”. When a bias voltage greater than a threshold voltage (V_(t)) (i.e., turn-on voltage) for the transistor 100 is applied to the gate electrode 108 along with a concurrently applied bias voltage between the source and drain regions 110, 112, an electric current (e.g., a transistor drive current) flows between the source and drain regions 110, 112 through the channel region 114. The amount of drive current developed for a given bias voltage (e.g., applied to the gate electrode 108 or between the source and drain regions 110, 112) is a function of, among others, the mobility of the material used to form the channel region 114. In some examples, the channel region 114 includes silicon (Si) and/or a high-mobility material such as germanium, as well as any of the plurality of compound semiconductors or alloy semiconductors as known in the art. High-mobility materials include those materials with electron and/or hole mobility greater than silicon (Si), which has an intrinsic electron mobility at room temperature (300 K) of around 1350 cm²/V-s and a hole mobility of around 480 cm²/V-s.

Referring to FIG. 1B, illustrated therein is a FinFET device 150, providing an example of an alternative device type which may include embodiments of the present disclosure. By way of example, the FinFET device 100 includes one or more fin-based, multi-gate field-effect transistors (FETs). The FinFET device 100 includes a substrate 152, at least one fin element 154 extending from the substrate 152, isolation regions 156, and a gate structure 158 disposed on and around the fin-element 154. The substrate 152 may be a semiconductor substrate such as a silicon substrate. In various embodiments, the substrate 152 may be substantially the same as the substrate 102, as described above.

The fin-element 154, like the substrate 152, may comprise silicon or another elementary semiconductor, such as germanium; a compound semiconductor including silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, InGaAs, GaInP, and/or GaInAsP; or combinations thereof. The fins 154 may be fabricated using suitable processes including photolithography and etch processes. The photolithography process may include forming a photoresist layer (resist) overlying the substrate (e.g., on a silicon layer), exposing the resist to a pattern, performing post-exposure bake processes, and developing the resist to form a masking element including the resist. In some embodiments, pattering the resist to form the making element may be performed using an electron beam (e-beam) lithography process. The masking element may then be used to protect regions of the substrate while an etch process forms recesses into the silicon layer, thereby leaving an extending fin 154. The recesses may be etched using a dry etch (e.g., chemical oxide removal), a wet etch, and/or other suitable processes. Numerous other embodiments of methods to form the fins 154 on the substrate 152 may also be used.

Each of the plurality of fins 154 also include a source region 155 and a drain region 157 where the source/drain regions 155, 157 are formed in, on, and/or surrounding the fin 154. The source/drain regions 155, 157 may be epitaxially grown over the fins 154. In addition, a channel region of a transistor is disposed within the fin 154, underlying the gate structure 158, along a plane substantially parallel to a plane defined by section AA′ of FIG. 1B. In some examples, the channel region of the fin includes a high-mobility material, as described above.

The isolation regions 156 may be shallow trench isolation (STI) features. Alternatively, a field oxide, a LOCOS feature, and/or other suitable isolation features may be implemented on and/or within the substrate 152. The isolation regions 156 may be composed of silicon oxide, silicon nitride, silicon oxynitride, fluorine-doped silicate glass (FSG), a low-k dielectric, combinations thereof, and/or other suitable material known in the art. In an embodiment, the isolation structures are STI features and are formed by etching trenches in the substrate 152. The trenches may then be filled with isolating material, followed by a chemical mechanical polishing (CMP) process. However, other embodiments are possible. In some embodiments, the isolation regions 156 may include a multi-layer structure, for example, having one or more liner layers.

The gate structure 158 includes a gate stack having an interfacial layer 160 formed over the channel region of the fin 154, a gate dielectric layer 162 formed over the interfacial layer 160, and a metal layer 164 formed over the gate dielectric layer 162. In various embodiments, the interfacial layer 160 is substantially the same as the interfacial layer described as part of the gate dielectric 106. In some embodiments, the gate dielectric layer 162 is substantially the same as the gate dielectric 106 and may include high-k dielectrics similar to that used for the gate dielectric 106. Similarly, in various embodiments, the metal layer 164 is substantially the same as the gate electrode 108, described above. In some embodiments, sidewall spacers are formed on sidewalls of the gate structure 158. The sidewall spacers may include a dielectric material such as silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, or combinations thereof.

Embodiments of the present disclosure offer advantages over the existing art, though it is understood that other embodiments may offer different advantages, not all advantages are necessarily discussed herein, and no particular advantage is required for all embodiments. For example, embodiments discussed herein include methods and structures directed to a pre-deposition treatment (e.g., of a work-function layer), for example to reduce a thickness of the work-function layer prior to a subsequent atomic layer deposition (ALD) process (e.g., subsequent ALD metal layer deposition), and the structures formed thereby. In some embodiments, the pre-deposition treatment (pre-treatment) and subsequent ALD process may be performed in-situ. In some cases, the pre-treatment and subsequent ALD metal layer deposition process may not be performed sequentially and in-situ. As used herein, the term “in-situ” is used to describe processes that are performed while a device or substrate remains within a processing system (e.g., including a load lock chamber, transfer chamber, processing chamber, or any other fluidly coupled chamber), and where for example, the processing system allows the substrate to remain under vacuum conditions. As such, the term “in-situ” may also generally be used to refer to processes in which the device or substrate being processed is not exposed to an external ambient (e.g., external to the processing system). In addition, while embodiments of the present disclosure may be primarily discussed with reference to N-type transistors, it will be understood that the embodiments disclosed herein may equally be applied to P-type transistors, where such implementations can be readily deduced by one skilled in the art, for example by symmetry to the N-type device implementations discussed below.

At least some embodiments of the present disclosure are directed to work function tuning for devices manufactured using a 10 nanometer or 7 nanometer process technology, although it will be understood that embodiments disclosed herein may be equally applied to other process technologies without departing from the scope of the present disclosure. In addition, embodiments of the present disclosure may be simultaneously used to ameliorate gap fill impact (e.g., by use of ALD processing). As used herein, the term “gap fill impact” may be used to describe the challenge of gate metal fill (e.g., in a replacement metal gate process). In some existing processes, poor metal gate deposition may cause gaps or voids in the metal gate, detrimentally impacting device performance. Embodiments of the present disclosure, which advantageously use ALD processing for metal gate layer deposition, provide high-quality, conformal metal gate layers that may be substantially void-free and thereby effectively mitigate potential problems associated with the gap fill impact. Additionally, in at least some existing processes (e.g., some 10 or 7 nanometer processes), the effective work function is limited by lack of an adequate tuning knob. Thus, there is a need for an effective work function tuning knob to further enhance device performance, for example, that goes beyond the traditional work function tuning approach of layer thickness adjustment. For example, in at least some existing processes (e.g., which employ ALD for gate stack deposition), work function tuning may be achieved by deposition of more ALD cycles to reduce metal surface loading effects.

As described above, embodiments of the present disclosure are directed to a pre-deposition treatment (e.g., of a work-function layer) and subsequent ALD process, and the structures formed thereby. As used herein, the term “pre-deposition treatment” may be used interchangeably with the terms “pre-treatment”, “pre-deposition soak”, or “pre-soak”. Thus, various embodiments disclosed herein are based on cleaning an oxidized surface (e.g., of a work-function layer, upon which an ALD metal film will be subsequently deposited) by using a chlorine [Cl] and/or fluorine [F]-based metal precursor pre-soak or pre-treatment process. By employing this pre-soak/pre-treatment process, the work function of the subsequently deposited ALD metal film will not depend on a varying substrate surface or quality of an underlying substrate (e.g., such as an underlying work-function layer having an oxidized layer) that can reduce the growth rate (and thus the thickness) of the ALD metal film, thereby resulting in an improved device threshold voltage (Vt). Thus, at least some advantages of the present disclosure include improving device Vt by using a [Cl] and/or [F]-based metal precursor pre-soak process to treat a work function setting layer (e.g., N-type work function layer), prior to deposition of an appropriate next metal layer (e.g. another work-function layer, barrier layer, cap layer, or other appropriate next metal layer), performed together/sequentially (e.g., in-situ) in a processing system such as a cluster tool (e.g., an ALD cluster tool where chambers are clustered together). To be sure, in some embodiments, a separate ex-situ pre-treatment (e.g., of the work-function layer) followed by deposition of the next metal layer may provide some advantages as well (e.g., threshold voltage improvement).

As described below, the [Cl] and/or [F]-based metal precursor pre-treatment process disclosed herein may not only be used to clean a surface oxide layer (e.g., of an underlying work-function metal layer), but embodiments disclosed herein may further advantageously use the pre-treatment process to reduce a thickness of the underlying work-function metal layer prior to deposition of the next metal layer, so as to improve Vt. By way of example, in some embodiments, a work function value, for example of the work-function layer, is dependent on the thickness of the work function layer. Thus, reduction of the thickness of the work function layer may change the value of the work function of the work-function layer, and thereby change (improve) the value of the threshold voltage (Vt). It is also noted that the term “reducing the thickness”, as used herein, may be used to describe a process by which a first layer (having a first layer thickness) of a metal layer (having an first total thickness, where the first layer thickness is less than the first total thickness) becomes oxidized, and where the oxidized first layer is removed (e.g., by the pre-treatment process described herein), such that the metal layer has a second total thickness less than the first total thickness (after removal of the oxidized first layer).

Stated in another way, based on free oxide by using [Cl]/[F]-based metal precursor pre-soak to clean up on oxidation surface of ALD metal film surface, the next work function of ALD metal film will not depend on different substrates to reduce their thickness growth rate and also get Vt improved. Vt will be improved by using [Cl]/[F]-based metal precursor pre-soak process and N-metal Work function layer-chamber clustered together.

Referring now to FIG. 2, illustrated is a method 200 of performing a pre-deposition treatment (e.g., of the work-function layer), for example to reduce a thickness of the work-function layer prior to a subsequent ALD process, in accordance with some embodiments. The method 200 may be implemented on a single-gate planar device, such as the exemplary transistor 100 described above with reference to FIG. 1A, as well as on a multi-gate device, such as the FinFET device 150 described above with reference to FIG. 1B. Thus, one or more aspects discussed above with reference to the transistor 100 and/or the FinFET 150 may also apply to the method 200. To be sure, in various embodiments, the method 200 may be implemented on other devices such as gate-all-around (GAA) devices, Omega-gate (Ω-gate) devices, or Pi-gate (Π-gate) devices, as well as strained-semiconductor devices, silicon-on-insulator (SOI) devices, partially-depleted SOI devices, fully-depleted SOI devices, or other devices as known in the art.

It is understood that parts of the method 200 and/or any of the exemplary transistor devices discussed with reference to the method 200 may be fabricated by a well-known complementary metal-oxide-semiconductor (CMOS) technology process flow, and thus some processes are only briefly described herein. Further, it is understood that any exemplary transistor devices discussed herein may include various other devices and features, such as additional transistors, bipolar junction transistors, resistors, capacitors, diodes, fuses, etc., but are simplified for a better understanding of the inventive concepts of the present disclosure. Further, in some embodiments, the exemplary transistor device(s) disclosed herein may include a plurality of semiconductor devices (e.g., transistors), which may be interconnected. In addition, in some embodiments, various aspects of the present disclosure may be applicable to either one of a gate-last process or a gate-first process.

In addition, in some embodiments, the exemplary transistor devices illustrated herein may include a depiction of a device at an intermediate stage of processing, as may be fabricated during processing of an integrated circuit, or portion thereof, that may comprise static random access memory (SRAM) and/or other logic circuits, passive components such as resistors, capacitors, and inductors, and active components such as P-channel field-effect transistors (PFETs), N-channel FETs (NFETs), metal-oxide-semiconductor field-effect transistors (MOSFETs), complementary metal-oxide-semiconductor (CMOS) transistors, bipolar transistors, high voltage transistors, high frequency transistors, other memory cells, and/or combinations thereof.

Referring first to the method 200, the method 200 provides a general process flow for performing a pre-deposition treatment (e.g., of the work-function layer), for example to reduce a thickness of the work-function layer prior to a subsequent ALD process, in accordance with some embodiments. Additional details of the processes and exemplary related structures according to embodiments of the present disclosure are discussed in more detail below with reference to the examples of FIGS. 3 and 4. The method 200 begins at block 202 where an interfacial layer is formed over the substrate 102, where the formed interfacial layer may be substantially similar to the interfacial layer described above as part of the gate dielectric 106. The method 200 proceeds to block 204 where a high-K dielectric layer is formed on the interfacial layer, where the high-K dielectric layer may be substantially similar to the high-K dielectric layer described above as part of the gate dielectric 106. In some cases, a high-K capping layer may be formed over the high-K dielectric layer.

After formation of the high-K dielectric layer, the method 200 then proceeds to block 206 where a work-function metal is deposited over the high-K dielectric layer. In some embodiments, the work-function metal is part of the gate electrode 108 described above with reference to FIG. 1A. Alternatively, in some embodiments, the work-function metal is part of the metal layer 164 described above with reference to FIG. 1B. As used herein, the term “work-function metal” is used to describe a layer which is used to set a value of the work function of the gate electrode 108. In various embodiments, the work-function metal may include TiN, TaN, TiAlC, TiAl, TiSiN, TaSi, TiAlN, a combination thereof, or other appropriate metal. Thus, in some embodiments, the work-function metal layer deposited over the high-K dielectric layer may include a plurality of layers configured to set the value of the work function of the gate electrode 108. In various examples, the work-function metal may be formed using ALD. By way of example, the work-function metal may be deposited by ALD at a temperature from about 200-600° C. In some cases, the work-function metal may alternately be formed using PVD, CVD, electron beam (e-beam) evaporation, and/or other suitable process. In some embodiments, a surface of the deposited work-function metal (e.g., deposited by ALD) may oxidize (e.g., due to exposure to an external ambient after deposition of the work-function metal), forming an ALD metal oxidation surface on the work-function metal layer.

In at least some existing processes, oxidation of the work-function metal (formation of the ALD metal oxidation surface) may result in a loading effect for a metal layer subsequently deposited on the oxidized work-function metal. As used herein, the term “loading effect” is used to describe an unwanted alteration of characteristics/properties of the metal layer deposited onto the oxidized work-function metal as a result of the oxidized work-function metal. Embodiments of the present disclosure provide for the removal (or substantial removal) of the oxidized layer of the work-function metal prior to the deposition of a subsequent metal layer, thereby preserving the desired characteristics/properties of the subsequently deposited metal layer. In some cases, concurrently with and as a result of removal the oxidized layer of the work-function metal, the pre-treatment process may be used to reduce the thickness of the underlying work-function metal layer prior to deposition of the next metal layer.

The method 200 then proceeds to block 208 where a pre-treatment process of the work-function metal is performed to reduce a thickness of the work-function metal. In an embodiment of the block 208, the ALD metal oxidation surface (e.g., the oxidized layer of the work-function metal) may be removed by a pre-treatment process that includes a Cl-based or F-based metal precursor to treat the ALD metal oxidation surface, and reduce the thickness of the work-function metal, before depositing a subsequent metal film over the work-function metal. In some embodiments, the Cl-based or F-based metal precursor includes TiCl_(x), TaCl_(x), TiF_(x), HfCl_(x), WF_(x) or WCl_(x), where ‘x’ is equal to about 1-6. In various embodiments, the pre-treatment process, and the metal film deposition which follows, is an in-situ process, for example, performed within a processing system such as an ALD cluster tool. By way of example, and during the pre-treatment process, the Cl-based or F-based metal precursor may be introduced into a processing chamber of the processing system (e.g., where the processing chamber houses the substrate having the ALD metal oxidation surface), for example, at a pre-treatment processing temperature of about 300-1000° C., and at a flow rate of about 100-8000 standard cubic centimeters per minute (sccm). In various examples, the pre-treatment processing conditions (e.g., including selection of the Cl-based or F-based metal precursor, pre-treatment temperature, and flow rate of the Cl-based or F-based metal precursor) are selected so as to induce a thermal chemical reaction between the Cl-based or F-based metal precursor and the ALD metal oxidation surface, such that as a result of the pre-treatment process, the oxidized layer of the work-function metal is removed or cleaned off, thereby leaving behind an non-oxidized, clean work-function metal surface. Moreover, in some embodiments and also as a result of the pre-treatment process, the thickness of the work-function metal (or other metal treated by the pre-treatment process) is reduced. To be sure, in some embodiments, a separate ex-situ pre-treatment (e.g., of the work-function layer) followed by deposition of the next metal layer may provide some advantages as well (e.g., threshold voltage improvement).

After the pre-treatment process, the method 200 then proceeds to block 210 where a next (subsequent) metal layer is deposited over the pre-treated, thinned work-function metal layer. In some embodiments, the next metal layer includes an N-metal layer (e.g., such as TiAlC), which may be deposited by ALD. In some cases, a TiN layer may optionally be deposited over the N-metal layer, and such a TiN layer may also be deposited by ALD. In addition, in some examples, such a TiN layer may be deposited sequentially, in-situ after deposition of the N-metal layer. By way of example, and in some embodiments, the next metal layer (and the optionally subsequently deposited TiN layer) may also be part of the gate electrode 108 described above with reference to FIG. 1A. Alternatively, in some embodiments, the next metal layer may also be part of the metal layer 164 described above with reference to FIG. 1B. Additionally, in some embodiments, the next metal layer(s) deposited over the pre-treated work-function layer may include one or more other layers (e.g., in addition those described above). In some cases, the next metal layer(s) and any other layers deposited over the pre-treated work-function layer may also be used to set the value of the work function of the gate electrode 108. Of particular note, since the oxidized layer of the work-function metal was cleaned/removed during the pre-treatment process, as described above, the next metal layer may be deposited onto the non-oxidized, clean work-function metal surface. As such, the desired characteristics/properties of the deposited next metal layer are preserved, as the next metal layer is not subject to loading effects (e.g., due to an oxidized layer) of the underlying work-function metal. As a further result, embodiments of the present disclosure result in devices (e.g., the transistor 100) having improved threshold voltage and improved device reliability. Moreover, as discussed above, the pre-treatment process may also reduce the thickness of the work-function metal (or other metal treated by the pre-treatment process). Stated another way, by performing the pre-treatment process as described herein, the thickness of the work-function layer may be reduced, and the subsequently deposited N-metal layer may be thicker (e.g., than for an N-metal layer deposited on a non-pre-treated work-function layer) while using substantially the same number of ALD growth cycles to deposit the N-metal layer. Generally, performing the pre-treatment process as described herein, may result in the reduction of the thickness of the work function layer and may change the value of the work function of the work-function layer, and thereby change (improve) the value of the threshold voltage (Vt).

The device (e.g., the transistor 100) fabricated according to the method 200 may undergo further processing to form various features and regions known in the art. For example, subsequent processing may form various contacts/vias/lines and multilayers interconnect features (e.g., metal layers and interlayer dielectrics) on the substrate including the device, configured to connect the various features to form a functional circuit that may include one or more devices (e.g., one or more transistors 100). In furtherance of the example, a multilayer interconnection may include vertical interconnects, such as vias or contacts, and horizontal interconnects, such as metal lines. The various interconnection features may employ various conductive materials including copper, tungsten, and/or silicide. In one example, a damascene and/or dual damascene process is used to form a copper related multilayer interconnection structure. Moreover, additional process steps may be implemented before, during, and after the method 200, and some process steps described above may be replaced or eliminated in accordance with various embodiments of the method 200. As a further example, in various embodiments, the method 200 may be applied to the formation of a gate stack which may be used for an N-type ultra-low threshold voltage (N-uLVT) device or for the formation of a gate stack which may be used for an N-type standard threshold voltage (N-SVT) device, among others.

Referring now to FIGS. 3 and 4, illustrated therein are cross-sectional transmission electron microscope (TEM) images for a device processed without performing a pre-treatment process (FIG. 3), and for a device processed using a pre-treatment process (FIG. 4), in accordance with embodiments disclosed herein. It is noted that FIGS. 3 and 4 illustrate exemplary compositions for the stack-up of layers (e.g., for a metal gate stack). These exemplary compositions are provided merely for ease of reference and not intended to be limiting beyond what is specifically claimed. Various compositions within the scope of the present disclosure may include (e.g., within a single gate stack) one or more work-function layers, one or more barrier layers, one or more capping layers, one or more metal fill layers, one or more polysilicon layers, one or more silicide layers, one or more doped layers, or other appropriate layers, including and/or beyond those layers that are specifically mentioned herein, and which may be configured as necessary or desired for a given technology or application. Additionally, in some embodiments, the pre-treatment process and subsequent metal layer deposition processes described herein may be repeated multiple times for a given gate stack. In some examples, the pre-treatment process may be repeated multiple times to treat a particular metal layer (e.g., a particular work-function metal layer) prior to deposition of a subsequent metal layer.

For clarity of discussion, it is noted that transistor threshold voltage (Vt) and flatband voltage (Vfb) may be generally expressed as:

$V_{t} = {V_{fb} + \frac{\sqrt{2\; q\;\epsilon\; N_{A}2\varphi_{B}}}{C_{ox}}}$ $V_{fb} = {\varphi_{ms} + {2\varphi_{B}} - \frac{Q_{f}}{C_{ox}}}$ From these two expressions for Vt and Vfb, it is clear that Vt is affected by changes in the flatband voltage, and the flatband voltage is dependent on the work function φ_(ms).

Referring first to the exemplary composition of FIG. 3, illustrated therein is a structure including a TiAlC layer over a TaN layer. In some cases, the TaN layer may be the work-function layer described above, the TiAlC layer may be the N-metal layer described above. In various examples, the TaN layer and the TiAlC layer may be part of the gate electrode 108 or the metal layer 164 described above with reference to FIG. 1A and FIG. 1B, respectively. As shown, and in some embodiments, the TaN layer may have a thickness of about 16 Angstroms, and the TiAlC may have a thickness of about 42 Angstroms. It is noted that for the exemplary structure of FIG. 3 a pre-treatment process as described herein has not been performed. Thus, for example, after deposition of the TaN layer, the TiAlC may be directly deposited over the TaN layer without performing a pre-treatment process. It is noted, as described above, that a work function value of the TaN layer, is dependent on the thickness of the TaN layer. Thus, a value of the work function for the exemplary structure of FIG. 3 will be based at least in part on the thickness of the TaN layer, which in turn will at least in part determine the flatband voltage (Vfb), which in turn will at least in part determine a threshold voltage for a device include the exemplary structure of FIG. 3.

Referring next to the exemplary composition of FIG. 4, illustrated therein is a structure including a TiAlC layer over a TaN layer, similar to the exemplary structure of FIG. 3. In various examples, the TaN layer and the TiAlC layer may be part of the gate electrode 108 or the metal layer 164 described above with reference to FIG. 1A and FIG. 1B, respectively. In contrast to the example of FIG. 3, for the exemplary structure of FIG. 4 a pre-treatment process, as described herein, is performed to treat the TaN layer (e.g., the work-function layer) of a high-K (HK)/metal gate (MG) stack prior to deposition of the TiAlC layer. In various embodiments, the pre-treatment process performed to treat the TaN layer may include an ex situ or in-situ pre-treatment process. In the example of FIG. 4, the pre-treatment process applied to the TaN layer may include a WCl_(x) gas treatment. However, as described above, other [Cl] and/or fluorine [F]-based metal precursors may be used to perform the pre-treatment process described herein. For example, in some embodiments, the Cl-based or F-based metal precursor may include TiCl_(x), TaCl_(x), TiF_(x), HfCl_(x), WF_(x) or WCl_(x), where ‘x’ is equal to about 1-6. As a result of the pre-treatment process, a portion of the TaN layer (which may have been previously oxidized) may be removed, such that a thickness of the TaN layer is reduced (e.g., to about 8-10 Angstroms). In some embodiments, the TiAlC may be deposited (e.g., by ALD) sequentially, and in some cases in situ, after performing the pre-treatment of the TaN layer. In some embodiments, the deposited TiAlC layer may thus be thicker than for the example of FIG. 3, which did not include the pre-treatment process. Moreover, in various embodiments, a number of growth ALD growth cycles for the TiAlC layer for both of the exemplary structures of FIGS. 3 and 4 may be substantially the same. Stated another way, by performing the pre-treatment process as described herein, the thickness of the TaN layer may be reduced, and the subsequently deposited TiAlC layer may be thicker (than the non-pre-treated case) while using substantially the same number of ALD growth cycles to deposit the TiAlC layer. As noted above, the work function value of the TaN layer is dependent on the thickness of the TaN layer. Thus, a value of the work function for the exemplary structure of FIG. 4 will be different than the work function value for the exemplary structure of FIG. 3, based at least in part on the reduced thickness of the TaN layer, which in turn will affect the flatband voltage (Vfb) and the threshold voltage for a device including the exemplary structure of FIG. 4. Generally, performing the pre-treatment process as described herein, may result in the reduction of the thickness of the work function layer and may change the value of the work function of the work-function layer, and thereby change (improve) the value of the threshold voltage (Vt).

Referring now to FIG. 5, illustrated therein is a schematic top-view diagram of an exemplary multi-chamber processing system 500. In some embodiments, the system 500 may be equivalently referred to as a “cluster tool”. The system 500 may generally include load lock chambers 502, 504, a wafer handling chamber 506, and a plurality of processing chambers 1-6. In various embodiments, the load lock chambers 502, 504 provide for the transfer of substrates into and out of the system 500. In various embodiments, the system 500 is under vacuum, and the load lock chambers 502, 504 may “pump down” the substrates introduced into the system 500 (e.g., by way of a mechanical pump and/or a turbomolecular pump). In some embodiments, the load lock chambers 502, 504 may be adapted to receive a single wafer or a plurality of wafers (e.g., loaded into a cassette). By way of example, the load lock chambers 502, 504 may be separated from the wafer handling chamber 506 by way of a gate valve, allowing the wafer handling chamber 506 to remain under vacuum when one or both of the load lock chambers 502, 504 are vented.

In various embodiments, the wafer handling chamber 506 is equipped with an automated, robotic arm that may move smoothly along any of a horizontal, vertical, and/or rotational axis so as to transfer substrates between the load lock chambers 502, 504 and any of the substrate processing chambers 1-6. Each processing chamber 1-6 may be configured to perform a number of substrate processing operations such as atomic layer deposition (ALD), CVD, PVD, etching, pre-treatment/pre-soak, de-gassing, annealing, as well as a number of metrology operations such as XPS analysis, AFM analysis, and/or other suitable processing or metrology operations. In various embodiments, the system 500 may have more or less processing chambers, for example, as necessary for a particular process to be performed by the system 500.

The various embodiments described herein offer several advantages over the existing art. It will be understood that not all advantages have been necessarily discussed herein, no particular advantage is required for all embodiments, and other embodiments may offer different advantages. As one example, embodiments discussed herein include methods and structures directed to a pre-deposition treatment (e.g., of a work-function layer), for example to reduce a thickness of the work-function layer prior to a subsequent atomic layer deposition (ALD) process (e.g., subsequent ALD metal layer deposition) over the pre-treated layer. In addition, embodiments of the present disclosure may be effectively employed to accomplish work function tuning. For example, in various embodiments, reduction of the thickness of the work function layer may change the value of the work function of the work-function layer, and thereby change (improve) the value of the threshold voltage (Vt). In various embodiments, the pre-deposition treatment process (pre-treatment process) includes treating an oxidized surface (e.g., of a work-function layer) by using a chlorine [Cl] and/or fluorine [F]-based metal precursor pre-soak or pre-treatment process. The pre-treatment process described herein may effectively mitigate metal surface loading effects (e.g., of the work-function layer), thereby resulting in an improved device threshold voltage (Vt). Thus, at least some advantages of the present disclosure include improving device Vt by using a [Cl] and/or [F]-based metal precursor pre-soak process to treat (and thin) a work function setting layer (e.g., N-type work function layer), prior to deposition of an appropriate next metal layer (e.g. another work-function layer, barrier layer, cap layer, or other appropriate next metal layer), which may be performed together/sequentially (e.g., in-situ) in a processing system such as a cluster tool (e.g., an ALD cluster tool where chambers are clustered together). Embodiments of the present disclosure may also be simultaneously used to ameliorate gap fill impact (e.g., by use of ALD processing), as described above. To be sure, in some embodiments, a separate ex-situ pre-treatment (e.g., of the work-function layer) followed by deposition of the next metal layer may provide some advantages as well (e.g., threshold voltage improvement).

Thus, one of the embodiments of the present disclosure described a method for fabricating a semiconductor device, where the method includes forming a gate dielectric layer over a substrate, and depositing a work-function metal layer over the gate dielectric layer. In various examples, the work-function metal layer has a first thickness. Thereafter, a pre-treatment process of the work-function metal layer is performed, where the pre-treatment process removes an oxidized layer from a top surface of the work-function metal layer to form a treated work-function metal layer. By way of example, the treated work-function metal layer has a second thickness less than the first thickness. In various embodiments, after performing the pre-treatment process, another metal layer is deposited over the treated work-function metal layer.

In another of the embodiments, discussed is a method where a work-function metal layer is formed over a gate dielectric layer, and where the work-function metal layer has a first thickness. In some examples, a surface layer of the work-function metal layer is oxidized (e.g., by exposure to an ambient atmosphere). In some embodiments, the oxidized surface layer may be removed in a first chamber of a processing system, thereby forming a thinned work-function metal layer. In some cases, the thinned work-function metal layer has a second thickness less than the first thickness. Thereafter, while maintaining a vacuum condition of the processing system, a subsequent metal layer is deposited over the thinned work-function metal layer in a second chamber of the processing system.

In yet another of the embodiments, discussed is a device including a substrate having a gate stack formed thereon. By way of example, the device further includes a gate dielectric layer disposed over the substrate, a pre-treated work-function metal layer disposed over the gate dielectric layer, and a subsequent metal layer disposed over the pre-treated work-function metal layer. In various embodiments, the pre-treated work-function layer includes at least one of a Cl-based precursor treated layer and a F-based precursor treated layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of semiconductor device fabrication, comprising: forming a gate dielectric layer over a substrate; depositing a work-function metal layer over the gate dielectric layer, wherein the work-function metal layer has a first thickness; performing a pre-treatment process of the work-function metal layer, wherein the pre-treatment process removes an oxidized portion of the work-function metal layer from a top surface of the work-function metal layer to form a treated work-function metal layer, and wherein the treated work-function metal layer has a second thickness less than the first thickness; and after performing the pre-treatment process, depositing a TiAlC layer over the treated work-function metal layer.
 2. The method of claim 1, wherein the depositing the TiAlC layer is performed sequentially after the pre-treatment process while maintaining the substrate under a vacuum condition.
 3. The method of claim 1, wherein the pre-treatment process includes a precursor selected from the group consisting of: TiCl_(x), TaCl_(x), TiF_(x), HfCl_(x), WF_(x), and WCl_(x), wherein x is between approximately 1 and approximately
 6. 4. The method of claim 1, wherein the work-function metal layer includes at least one of TiN, TaN, TiAlC, TiAl, TiSiN, TaSi, and TiAlN.
 5. The method of claim 1, wherein the work-function metal layer and the TiAlC layer are deposited by atomic layer deposition.
 6. The method of claim 1, further comprising depositing a TiN layer over the TiAlC layer.
 7. The method of claim 1, wherein the pre-treatment process shifts a band edge of the work-function metal layer.
 8. The method of claim 1, wherein the second thickness is at least thirty percent less than the first thickness.
 9. A method of semiconductor device fabrication, comprising: forming a work-function metal layer over a gate dielectric layer, wherein the work-function metal layer has a first thickness; oxidizing a surface layer of the work-function metal layer; removing the oxidized surface layer in a first chamber of a processing system, thereby forming a thinned work-function metal layer, wherein the thinned work-function metal layer has a second thickness less than the first thickness; and while maintaining a vacuum condition of the processing system, depositing a subsequent metal layer over the thinned work-function metal layer in a second chamber of the processing system.
 10. The method of claim 9, wherein the removing the oxidized surface layer further includes removing the oxidized surface layer by way of a thermal chemical reaction between the oxidized surface layer and a precursor selected from the group consisting of: TiCl_(x), TaCl_(x), TiF_(x), HfCl_(x), WF_(x), and WCl_(x), wherein x is between approximately 1 and approximately
 6. 11. The method of claim 9, wherein the work-function metal layer includes at least one of TiN, TaN, TiAlC, TiAl, TiSiN, TaSi, and TiAlN.
 12. The method of claim 9, wherein the work-function metal layer is deposited at a temperature from approximately 200 degrees Celsius to approximately 600 degrees Celsius.
 13. The method of claim 10, wherein the thermal chemical reaction is performed at a temperature from approximately 300 degrees Celsius to approximately 1000 degrees Celsius, and wherein a flow rate of the precursor is between approximately 100 sccm and 8000 sccm.
 14. The method of claim 9, wherein the work-function metal layer includes an N-type work function metal layer.
 15. The method of claim 14, wherein the removing the oxidized surface layer shifts a conduction band edge of the N-type work-function metal layer.
 16. A method of semiconductor device fabrication, comprising: forming a gate stack over a substrate, wherein the forming the gate stack comprises: depositing a work-function metal layer, wherein the work-function metal layer has a first thickness; tuning a work-function value of the work-function metal layer by performing a pre-treatment process of the work-function metal layer, wherein the treated work-function metal layer has a second thickness less than the first thickness; and after tuning the work-function value of the work-function metal layer, depositing another metal layer over the treated work-function metal layer.
 17. The method of claim 16, wherein the forming the gate stack further comprises: prior to depositing the work-function metal layer, forming a gate dielectric layer over the substrate; and depositing the work-function metal layer over the gate dielectric layer.
 18. The method of claim 16, wherein the depositing another metal layer is performed sequentially after the tuning the work-function value while maintaining the substrate under a vacuum condition.
 19. The method of claim 16, wherein the pre-treatment process removes an oxidized layer from a top surface of the work-function metal layer to form the treated work-function metal layer.
 20. The method of claim 16, wherein the pre-treatment process includes a precursor selected from the group consisting of: TiCl_(x), TaCl_(x), TiF_(x), HfCl_(x), WF_(x), and WCl_(x), wherein x is between approximately 1 and approximately
 6. 